softmmu/icount.c

   1 /*
   2  * QEMU System Emulator
   3  *
   4  * Copyright (c) 2003-2008 Fabrice Bellard
   5  *
   6  * Permission is hereby granted, free of charge, to any person obtaining a copy
   7  * of this software and associated documentation files (the "Software"), to deal
   8  * in the Software without restriction, including without limitation the rights
   9  * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
  10  * copies of the Software, and to permit persons to whom the Software is
  11  * furnished to do so, subject to the following conditions:
  12  *
  13  * The above copyright notice and this permission notice shall be included in
  14  * all copies or substantial portions of the Software.
  15  *
  16  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
  17  * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
  18  * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
  19  * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
  20  * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
  21  * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
  22  * THE SOFTWARE.
  23  */
  24
  25 #include "qemu/osdep.h"
  26 #include "qemu/cutils.h"
  27 #include "migration/vmstate.h"
  28 #include "qapi/error.h"
  29 #include "qemu/error-report.h"
  30 #include "exec/exec-all.h"
  31 #include "sysemu/cpus.h"
  32 #include "sysemu/qtest.h"
  33 #include "qemu/main-loop.h"
  34 #include "qemu/option.h"
  35 #include "qemu/seqlock.h"
  36 #include "sysemu/replay.h"
  37 #include "sysemu/runstate.h"
  38 #include "hw/core/cpu.h"
  39 #include "sysemu/cpu-timers.h"
  40 #include "sysemu/cpu-throttle.h"
  41 #include "timers-state.h"
  42
  43 /*
  44  * ICOUNT: Instruction Counter
  45  *
  46  * this module is split off from cpu-timers because the icount part
  47  * is TCG-specific, and does not need to be built for other accels.
  48  */
  49 static bool icount_sleep = true;
  50 /* Arbitrarily pick 1MIPS as the minimum allowable speed.  */
  51 #define MAX_ICOUNT_SHIFT 10
  52
  53 /*
  54  * 0 = Do not count executed instructions.
  55  * 1 = Fixed conversion of insn to ns via "shift" option
  56  * 2 = Runtime adaptive algorithm to compute shift
  57  */
  58 int use_icount;
  59
  60 static void icount_enable_precise(void)
  61 {
  62     use_icount = 1;
  63 }
  64
  65 static void icount_enable_adaptive(void)
  66 {
  67     use_icount = 2;
  68 }
  69
  70 /*
  71  * The current number of executed instructions is based on what we
  72  * originally budgeted minus the current state of the decrementing
  73  * icount counters in extra/u16.low.
  74  */
  75 static int64_t icount_get_executed(CPUState *cpu)
  76 {
  77     return (cpu->icount_budget -
  78             (cpu_neg(cpu)->icount_decr.u16.low + cpu->icount_extra));
  79 }
  80
  81 /*
  82  * Update the global shared timer_state.qemu_icount to take into
  83  * account executed instructions. This is done by the TCG vCPU
  84  * thread so the main-loop can see time has moved forward.
  85  */
  86 static void icount_update_locked(CPUState *cpu)
  87 {
  88     int64_t executed = icount_get_executed(cpu);
  89     cpu->icount_budget -= executed;
  90
  91     qatomic_set_i64(&timers_state.qemu_icount,
  92                     timers_state.qemu_icount + executed);
  93 }
  94
  95 /*
  96  * Update the global shared timer_state.qemu_icount to take into
  97  * account executed instructions. This is done by the TCG vCPU
  98  * thread so the main-loop can see time has moved forward.
  99  */
 100 void icount_update(CPUState *cpu)
 101 {
 102     seqlock_write_lock(&timers_state.vm_clock_seqlock,
 103                        &timers_state.vm_clock_lock);
 104     icount_update_locked(cpu);
 105     seqlock_write_unlock(&timers_state.vm_clock_seqlock,
 106                          &timers_state.vm_clock_lock);
 107 }
 108
 109 static int64_t icount_get_raw_locked(void)
 110 {
 111     CPUState *cpu = current_cpu;
 112
 113     if (cpu && cpu->running) {
 114         if (!cpu->can_do_io) {
 115             error_report("Bad icount read");
 116             exit(1);
 117         }
 118         /* Take into account what has run */
 119         icount_update_locked(cpu);
 120     }
 121     /* The read is protected by the seqlock, but needs atomic64 to avoid UB */
 122     return qatomic_read_i64(&timers_state.qemu_icount);
 123 }
 124
 125 static int64_t icount_get_locked(void)
 126 {
 127     int64_t icount = icount_get_raw_locked();
 128     return qatomic_read_i64(&timers_state.qemu_icount_bias) +
 129         icount_to_ns(icount);
 130 }
 131
 132 int64_t icount_get_raw(void)
 133 {
 134     int64_t icount;
 135     unsigned start;
 136
 137     do {
 138         start = seqlock_read_begin(&timers_state.vm_clock_seqlock);
 139         icount = icount_get_raw_locked();
 140     } while (seqlock_read_retry(&timers_state.vm_clock_seqlock, start));
 141
 142     return icount;
 143 }
 144
 145 /* Return the virtual CPU time, based on the instruction counter.  */
 146 int64_t icount_get(void)
 147 {
 148     int64_t icount;
 149     unsigned start;
 150
 151     do {
 152         start = seqlock_read_begin(&timers_state.vm_clock_seqlock);
 153         icount = icount_get_locked();
 154     } while (seqlock_read_retry(&timers_state.vm_clock_seqlock, start));
 155
 156     return icount;
 157 }
 158
 159 int64_t icount_to_ns(int64_t icount)
 160 {
 161     return icount << qatomic_read(&timers_state.icount_time_shift);
 162 }
 163
 164 /*
 165  * Correlation between real and virtual time is always going to be
 166  * fairly approximate, so ignore small variation.
 167  * When the guest is idle real and virtual time will be aligned in
 168  * the IO wait loop.
 169  */
 170 #define ICOUNT_WOBBLE (NANOSECONDS_PER_SECOND / 10)
 171
 172 static void icount_adjust(void)
 173 {
 174     int64_t cur_time;
 175     int64_t cur_icount;
 176     int64_t delta;
 177
 178     /* If the VM is not running, then do nothing.  */
 179     if (!runstate_is_running()) {
 180         return;
 181     }
 182
 183     seqlock_write_lock(&timers_state.vm_clock_seqlock,
 184                        &timers_state.vm_clock_lock);
 185     cur_time = REPLAY_CLOCK_LOCKED(REPLAY_CLOCK_VIRTUAL_RT,
 186                                    cpu_get_clock_locked());
 187     cur_icount = icount_get_locked();
 188
 189     delta = cur_icount - cur_time;
 190     /* FIXME: This is a very crude algorithm, somewhat prone to oscillation.  */
 191     if (delta > 0
 192         && timers_state.last_delta + ICOUNT_WOBBLE < delta * 2
 193         && timers_state.icount_time_shift > 0) {
 194         /* The guest is getting too far ahead.  Slow time down.  */
 195         qatomic_set(&timers_state.icount_time_shift,
 196                     timers_state.icount_time_shift - 1);
 197     }
 198     if (delta < 0
 199         && timers_state.last_delta - ICOUNT_WOBBLE > delta * 2
 200         && timers_state.icount_time_shift < MAX_ICOUNT_SHIFT) {
 201         /* The guest is getting too far behind.  Speed time up.  */
 202         qatomic_set(&timers_state.icount_time_shift,
 203                     timers_state.icount_time_shift + 1);
 204     }
 205     timers_state.last_delta = delta;
 206     qatomic_set_i64(&timers_state.qemu_icount_bias,
 207                     cur_icount - (timers_state.qemu_icount
 208                                   << timers_state.icount_time_shift));
 209     seqlock_write_unlock(&timers_state.vm_clock_seqlock,
 210                          &timers_state.vm_clock_lock);
 211 }
 212
 213 static void icount_adjust_rt(void *opaque)
 214 {
 215     timer_mod(timers_state.icount_rt_timer,
 216               qemu_clock_get_ms(QEMU_CLOCK_VIRTUAL_RT) + 1000);
 217     icount_adjust();
 218 }
 219
 220 static void icount_adjust_vm(void *opaque)
 221 {
 222     timer_mod(timers_state.icount_vm_timer,
 223                    qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL) +
 224                    NANOSECONDS_PER_SECOND / 10);
 225     icount_adjust();
 226 }
 227
 228 int64_t icount_round(int64_t count)
 229 {
 230     int shift = qatomic_read(&timers_state.icount_time_shift);
 231     return (count + (1 << shift) - 1) >> shift;
 232 }
 233
 234 static void icount_warp_rt(void)
 235 {
 236     unsigned seq;
 237     int64_t warp_start;
 238
 239     /*
 240      * The icount_warp_timer is rescheduled soon after vm_clock_warp_start
 241      * changes from -1 to another value, so the race here is okay.
 242      */
 243     do {
 244         seq = seqlock_read_begin(&timers_state.vm_clock_seqlock);
 245         warp_start = timers_state.vm_clock_warp_start;
 246     } while (seqlock_read_retry(&timers_state.vm_clock_seqlock, seq));
 247
 248     if (warp_start == -1) {
 249         return;
 250     }
 251
 252     seqlock_write_lock(&timers_state.vm_clock_seqlock,
 253                        &timers_state.vm_clock_lock);
 254     if (runstate_is_running()) {
 255         int64_t clock = REPLAY_CLOCK_LOCKED(REPLAY_CLOCK_VIRTUAL_RT,
 256                                             cpu_get_clock_locked());
 257         int64_t warp_delta;
 258
 259         warp_delta = clock - timers_state.vm_clock_warp_start;
 260         if (icount_enabled() == 2) {
 261             /*
 262              * In adaptive mode, do not let QEMU_CLOCK_VIRTUAL run too
 263              * far ahead of real time.
 264              */
 265             int64_t cur_icount = icount_get_locked();
 266             int64_t delta = clock - cur_icount;
 267             warp_delta = MIN(warp_delta, delta);
 268         }
 269         qatomic_set_i64(&timers_state.qemu_icount_bias,
 270                         timers_state.qemu_icount_bias + warp_delta);
 271     }
 272     timers_state.vm_clock_warp_start = -1;
 273     seqlock_write_unlock(&timers_state.vm_clock_seqlock,
 274                        &timers_state.vm_clock_lock);
 275
 276     if (qemu_clock_expired(QEMU_CLOCK_VIRTUAL)) {
 277         qemu_clock_notify(QEMU_CLOCK_VIRTUAL);
 278     }
 279 }
 280
 281 static void icount_timer_cb(void *opaque)
 282 {
 283     /*
 284      * No need for a checkpoint because the timer already synchronizes
 285      * with CHECKPOINT_CLOCK_VIRTUAL_RT.
 286      */
 287     icount_warp_rt();
 288 }
 289
 290 void icount_start_warp_timer(void)
 291 {
 292     int64_t clock;
 293     int64_t deadline;
 294
 295     assert(icount_enabled());
 296
 297     /*
 298      * Nothing to do if the VM is stopped: QEMU_CLOCK_VIRTUAL timers
 299      * do not fire, so computing the deadline does not make sense.
 300      */
 301     if (!runstate_is_running()) {
 302         return;
 303     }
 304
 305     if (replay_mode != REPLAY_MODE_PLAY) {
 306         if (!all_cpu_threads_idle()) {
 307             return;
 308         }
 309
 310         if (qtest_enabled()) {
 311             /* When testing, qtest commands advance icount.  */
 312             return;
 313         }
 314
 315         replay_checkpoint(CHECKPOINT_CLOCK_WARP_START);
 316     } else {
 317         /* warp clock deterministically in record/replay mode */
 318         if (!replay_checkpoint(CHECKPOINT_CLOCK_WARP_START)) {
 319             /*
 320              * vCPU is sleeping and warp can't be started.
 321              * It is probably a race condition: notification sent
 322              * to vCPU was processed in advance and vCPU went to sleep.
 323              * Therefore we have to wake it up for doing someting.
 324              */
 325             if (replay_has_checkpoint()) {
 326                 qemu_clock_notify(QEMU_CLOCK_VIRTUAL);
 327             }
 328             return;
 329         }
 330     }
 331
 332     /* We want to use the earliest deadline from ALL vm_clocks */
 333     clock = qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL_RT);
 334     deadline = qemu_clock_deadline_ns_all(QEMU_CLOCK_VIRTUAL,
 335                                           ~QEMU_TIMER_ATTR_EXTERNAL);
 336     if (deadline < 0) {
 337         static bool notified;
 338         if (!icount_sleep && !notified) {
 339             warn_report("icount sleep disabled and no active timers");
 340             notified = true;
 341         }
 342         return;
 343     }
 344
 345     if (deadline > 0) {
 346         /*
 347          * Ensure QEMU_CLOCK_VIRTUAL proceeds even when the virtual CPU goes to
 348          * sleep.  Otherwise, the CPU might be waiting for a future timer
 349          * interrupt to wake it up, but the interrupt never comes because
 350          * the vCPU isn't running any insns and thus doesn't advance the
 351          * QEMU_CLOCK_VIRTUAL.
 352          */
 353         if (!icount_sleep) {
 354             /*
 355              * We never let VCPUs sleep in no sleep icount mode.
 356              * If there is a pending QEMU_CLOCK_VIRTUAL timer we just advance
 357              * to the next QEMU_CLOCK_VIRTUAL event and notify it.
 358              * It is useful when we want a deterministic execution time,
 359              * isolated from host latencies.
 360              */
 361             seqlock_write_lock(&timers_state.vm_clock_seqlock,
 362                                &timers_state.vm_clock_lock);
 363             qatomic_set_i64(&timers_state.qemu_icount_bias,
 364                             timers_state.qemu_icount_bias + deadline);
 365             seqlock_write_unlock(&timers_state.vm_clock_seqlock,
 366                                  &timers_state.vm_clock_lock);
 367             qemu_clock_notify(QEMU_CLOCK_VIRTUAL);
 368         } else {
 369             /*
 370              * We do stop VCPUs and only advance QEMU_CLOCK_VIRTUAL after some
 371              * "real" time, (related to the time left until the next event) has
 372              * passed. The QEMU_CLOCK_VIRTUAL_RT clock will do this.
 373              * This avoids that the warps are visible externally; for example,
 374              * you will not be sending network packets continuously instead of
 375              * every 100ms.
 376              */
 377             seqlock_write_lock(&timers_state.vm_clock_seqlock,
 378                                &timers_state.vm_clock_lock);
 379             if (timers_state.vm_clock_warp_start == -1
 380                 || timers_state.vm_clock_warp_start > clock) {
 381                 timers_state.vm_clock_warp_start = clock;
 382             }
 383             seqlock_write_unlock(&timers_state.vm_clock_seqlock,
 384                                  &timers_state.vm_clock_lock);
 385             timer_mod_anticipate(timers_state.icount_warp_timer,
 386                                  clock + deadline);
 387         }
 388     } else if (deadline == 0) {
 389         qemu_clock_notify(QEMU_CLOCK_VIRTUAL);
 390     }
 391 }
 392
 393 void icount_account_warp_timer(void)
 394 {
 395     if (!icount_sleep) {
 396         return;
 397     }
 398
 399     /*
 400      * Nothing to do if the VM is stopped: QEMU_CLOCK_VIRTUAL timers
 401      * do not fire, so computing the deadline does not make sense.
 402      */
 403     if (!runstate_is_running()) {
 404         return;
 405     }
 406
 407     /* warp clock deterministically in record/replay mode */
 408     if (!replay_checkpoint(CHECKPOINT_CLOCK_WARP_ACCOUNT)) {
 409         return;
 410     }
 411
 412     timer_del(timers_state.icount_warp_timer);
 413     icount_warp_rt();
 414 }
 415
 416 void icount_configure(QemuOpts *opts, Error **errp)
 417 {
 418     const char *option = qemu_opt_get(opts, "shift");
 419     bool sleep = qemu_opt_get_bool(opts, "sleep", true);
 420     bool align = qemu_opt_get_bool(opts, "align", false);
 421     long time_shift = -1;
 422
 423     if (!option) {
 424         if (qemu_opt_get(opts, "align") != NULL) {
 425             error_setg(errp, "Please specify shift option when using align");
 426         }
 427         return;
 428     }
 429
 430     if (align && !sleep) {
 431         error_setg(errp, "align=on and sleep=off are incompatible");
 432         return;
 433     }
 434
 435     if (strcmp(option, "auto") != 0) {
 436         if (qemu_strtol(option, NULL, 0, &time_shift) < 0
 437             || time_shift < 0 || time_shift > MAX_ICOUNT_SHIFT) {
 438             error_setg(errp, "icount: Invalid shift value");
 439             return;
 440         }
 441     } else if (icount_align_option) {
 442         error_setg(errp, "shift=auto and align=on are incompatible");
 443         return;
 444     } else if (!icount_sleep) {
 445         error_setg(errp, "shift=auto and sleep=off are incompatible");
 446         return;
 447     }
 448
 449     icount_sleep = sleep;
 450     if (icount_sleep) {
 451         timers_state.icount_warp_timer = timer_new_ns(QEMU_CLOCK_VIRTUAL_RT,
 452                                          icount_timer_cb, NULL);
 453     }
 454
 455     icount_align_option = align;
 456
 457     if (time_shift >= 0) {
 458         timers_state.icount_time_shift = time_shift;
 459         icount_enable_precise();
 460         return;
 461     }
 462
 463     icount_enable_adaptive();
 464
 465     /*
 466      * 125MIPS seems a reasonable initial guess at the guest speed.
 467      * It will be corrected fairly quickly anyway.
 468      */
 469     timers_state.icount_time_shift = 3;
 470
 471     /*
 472      * Have both realtime and virtual time triggers for speed adjustment.
 473      * The realtime trigger catches emulated time passing too slowly,
 474      * the virtual time trigger catches emulated time passing too fast.
 475      * Realtime triggers occur even when idle, so use them less frequently
 476      * than VM triggers.
 477      */
 478     timers_state.vm_clock_warp_start = -1;
 479     timers_state.icount_rt_timer = timer_new_ms(QEMU_CLOCK_VIRTUAL_RT,
 480                                    icount_adjust_rt, NULL);
 481     timer_mod(timers_state.icount_rt_timer,
 482                    qemu_clock_get_ms(QEMU_CLOCK_VIRTUAL_RT) + 1000);
 483     timers_state.icount_vm_timer = timer_new_ns(QEMU_CLOCK_VIRTUAL,
 484                                         icount_adjust_vm, NULL);
 485     timer_mod(timers_state.icount_vm_timer,
 486                    qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL) +
 487                    NANOSECONDS_PER_SECOND / 10);
 488 }